Light sensitive lamp control circuit



Apml 5, 1965 R. L. SEIDLER 9 3 LIGHT SENSITIVE LAMP CONTROL CIRCUIT Original Filed May 7, 1959 3 Sheets-Sheet 1 IIC FIG!

LIGHT CONTROL VOLTAGE ClRCUIT REGULATOR CIRCUIT FLASHER CIRCUITS LAMP CHANGER INVENTOR.

April 19% R. L. SEIDLER 3,244,892

LIGHT SENSITIVE LAMP CONTROL CIRCUIT Original Filed May 7, 1959 3 Sheets-Sheet 2 FREE RUNNING R RUNNING 1/2 .f/K EE {/4 1/5 NONO- STABLE FIG. 3

INVENTOR. 305587 A 52=40e April 5, 19% R. a... SEliDLE-ZR 3,244,892

LIGHT SENSITIVE LAMP CONTROL CIRCUIT Original Filed May 7, 1959 I5 Sheets-Sheet 3 LAMP CHANGER IN VENTOR'.

Boa-"er 1. 52/04 5/2 United States Patent 3 244,892 LIGHT SENSiTlVE I IAMP CONTRGL CIRCUIT Robert L. Seidler, Whippauy, N.J., assignor to Robert L. Seidler, Whippany, and Marvin Ross and Bertram Polow, both of Morristowu, N.J., trustees Original application May 7, 1959, Ser. No. 811,695, pow Patent No. 3,027,491, dated Mar. 27, 1962. Divided and this application Dec. 11, 1961, Ser. No. 158,459

4 Claims. (Cl. 250--214) This invention relates to a lamp control circuit which is operated by semi-conductor components and includes a control for lighting signal or illuminating lamps only when the ambient illumination is reduced below a predetermined level. The control circuit also relates to means for short and long flashing by the lamps in accordance with a predetermined program. This application is a division of an original application entitled Lamp Control Circuit filed May 7, 1959 under Serial No. 811,695, now Patent No, 3,027,491.

Many types of lamp control units have been made and used but nearly all these control systems have employed moving parts such as motors and relays, and nearly all prior art control circuits have contained electrical contacts which make and break electric circuits and are therefore subject to pitting, sparking, and short-circuiting. The present control circuit contains no moving parts and no electrical contacts. All switching operations and circuit variations are made by the means of semi-conductor components such as transistors and diodes and therefore have extremely long life and not subject to the disadvantages met in the usual type of control cir- ICUlI.

One of the objects of this invention is to provide an improved lamp circuit which avoids one or more of the disadvantages and limitations of prior art circuits.

Another object of the invention is to control the flashing of signal or illuminating lamps by sensing the value of the ambient illumination.

Another object of the invention is to turn the electrical power on and oil? at a predetermined rate to produce a flashing signal.

Another object of the invention is to permit adjustment of the various control circuits so that the light flashes produced by a lamp may include long and short alternate light signals.

Another object of the invention is to prevent the illumination produced by the flashing lamps from operating the light-sensitive circuit.

Another object of the invention is to regulate the voltage applied to the lamps.

Another object of the invention is to operate a motorized lamp changer when a lamp burns out.

Another object of the invention is to provide a lamp control circuit which is small, compact, has no mechanical moving parts, and has an exceedingly long life.

One feature of the invention includes a photoconductive cell which controls an amplifier and a switching transistor to turn the system on or off depending upon the value of steady ambient illumination.

A second feature of the invention includes three multivibrator circuits (generally called flip-flops) which operate together to produce light flashes having a predetermined frequency and a short-long program. The invention also includes a sensing device connected in series with the current supplied to the flashing lamps, the information of this sensing device being applied through a transistor to a lamp changer for changing lamps whenever the device is on and the current to the lamp is zero.

For a better understanding of the present invention, together with other and further objects thereof, refer- 3,244,892 Patented Apr. 5, 1966 ence is made to the following description taken in connection with the accompanying drawings.

FIGURE 1 is a schematic diagram of connections showing most of the circuits of the lamp control device in block form.

FIGURE 2 is a graph showing the current pulses produced by the three multivibrator circuits and the combination of all three.

FIGURES 3 and 4 when combined are a schematic diagram of the entire circuit showing in detail all the electrical components.

Referring now to FIGURE 1, the control circuit will be described in general in order to show the overall operation of the system. The circuit is powered by a direct current source of potential 10 which may be a battery. This source of potential is the only one needed in the entire circuit and provides electrical power for all the components including one or more lamps 11A, 11B and 11C. A photo-conductive cell 12 is employed to sense the ambient illumination and determine whether or not the lamps 11 should be turned on. The photo conductive cell 12 is connected to a light control circuit 13 which contains an amplifier unit and a switching transistor for controlling the other circuits in the system.

The lamp control circuit described herein includes three flasher circuits 14A, B and C; the combination of these circuits producing the novel short-long combination of signals shown in the last graph in FIGURE 2. It will be obvious that if such a combination of signals is not necessary and only symmetrical on and off signals are desired, only one free running multivibrator would be necessary. Group flashing may be obtained by using circuits 14A and 14B of FIGURE 1 as shown in a+b of FIGURE 2.

The pulses from the flasher circuits 14 are applied to a voltage regulator circuit 15 which regulates the voltage and applies a constant voltage to one of the lamps 11. The control circuit also includes a lamp changer circuit 16 which operates a motorized device to change the lamps after one has burned out. The invention herein described does not include the lamp changer nor any of its details. Many lamp changers have been devised and used. Some merely switch current from one lamp to another while other changers remove the damaged :or burned out lamp from a desired position in an optical system and replace another in the same position while at the same time switching electrical power to the new lamp. The present invention operates to supply a control voltage to the lamp changing device whenever zero current is sensed in the lamps circuit when the lamp should be lighted. In the drawing in FIGURE 1 (also FIGURE 4) the lamp changer circuit 16 is shown connected to a solenoid winding 17 which moves an armature 18, thereby actuating a lamp switch 24). It is to be understood that this simplified arrangement is for illustration only, and any other type of lamp changer can be used.

The light control circuit 13 receives its power from the emitter electrode of a transistor 21 shown in FIGURE 3 which acts as a simplified voltage regulator, supplying a regulated voltage to circuit 13 and also to the three multivibrator circuits 14A, 14B and 14C. Transistor 21 has its collector connected to the positive terminal of the source of potential while its base is connected to ground in series with a zener diode 22 which acts as a voltage reference. The regulated power applied to the multivibrator circuits on conductor 23 first passes through a filtering circuit including resistor 24 and capacitor 25.

This circuit eliminates transients from the ilasher circuits.

that otherwise might trigger the multivibrator when the lamps 11 are switched on and 011.

The light control circuit 13 is primarily controlled by the resistance of the ph-otoconductive cell 12. The output of circuit 13 is delivered over conductor 26 to the base of transistor 27 (FIGURE 4) which in turn controls other transistors to be described later. Circuit 13 includes transistors 39 and 31, the bases of which are connected to voltage divider circuits which include resistors connected between the positive source conductor 28 and the ground conductor 32. These resistors provide potentials to the bases of transistors 30 and 31 such that, when no light is incident on cell 12, transistor 30 is non-conductive, transistor 31 is conductive, and transistor 27 is non-conductive due to the bias current from transistor 31 through base resistor 33. As the amount of light incident on cell 12 increases, the resistance of the cell decreases and the Voltage of conductor 34 increases, causing an increase in voltage at the base of transistor 30, .through resistors 34A and 35. The application of this voltage is shunted by a time delay circuit composed of capacitor 36 and resistor 37 which prevents false operation by intermittent light flashes, such as lightning, moving auto headlights, etc. which do not affect the operation of this circuit because the voltage pulses produced by them are absorbed by capacitor 36. The transistor 46 serves to reduce the voltage at the phot-oconductive cell 12 thereby preventing transistor 3t) from conducting.

When transistor 30 starts to conduct, the voltage of its collector decreases causing a drop in the base current of transistor 31 supplied through resistors 40 and 41. This reduces the current through the collector-emitter circuit of transistor 31 and further increases the base current in transistor 30 by raising its base voltage through resistors 42, 43 and 35. Resistor 34A is made relatively high (100K) so that this action can proceed rapidly without charging capacitor 36. Diodes 44 and 45, in conjunction with resistors 41 and 43, prevent saturation of transistors 30 and 31, thereby improving the switching characteristics. In a similar manner, when the light incident on cell 12 decreases, a condition is reached where transistor 30 begins to turnofi and transistor 31 starts to turn on. The operation is then reversed and transistor 27 is made non-conductive.

The light control circuit 13 also includes two other transistors 46 and 47, having base voltages at the start of the cycle which cause transistor 46 to conduct and transistor 47 to be non-conductive. The base of transistor 47 is connected through resistor 48 to the collector of transistor 31, so that when transistor 31 is conducting, transistor 47 is non-conducting. Transistor 47 provides a resistance in parallel with the photocell 12 in series with a resistor 50 and transistor 46 and decreases the voltage applied to the base of transistor 30 through the photoconductive cell 12 thereby decreasing the differential between the values of ambient light required to turn the device on or off.

Transistor 46 has its emitter-collector circuit in series with the photoconductive cell 12 and operates to reduce the sensitivity of the control circuit when the signal lamps 11 are turned on. Due to this suppression, the device cannot turn itself ofi. In order to accomplish this result, the base of transistor 46 is connected by conductor 51 (in series with resistor 52) to the positive terminal (FIG- URE 4) 53 of the flasher. During the time the lamps are lighted, transistor 46 is made non-conductive and the resistance of cell 12 does not control the rest of circuit 13, thereby preventing turn off of the device While the lamp is flashing.

The flashing signals which turn the lamps 11 on and off are derived from three multivibrator circuits 14A, 14B and 14C. Circuit 14A is a free running multivibrator including transistors 54 and 55 with the usual capacity coupling between bases and collectors. This type of circuit is well known in the art and need not be described in detail. The rectifier diodes 110, 111, 112, 113, 114 and 115 are added to the circuit in order to prevent saturation and lock up when the power is applied initially. The

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output of this circuit is taken from point 56 and is applied over conductor 57 to the base of transistor 58, also over conductor 60 to the base of transistor 61. The output wave is shown graphically in curve a in FIGURE 2.

Transistor 61 is turned on and off, from full conduction to non-conduction, by the wave from circuit 14A, and this change of resistance is applied to the base bias circuit of a switching transistor 62. The base circuit of transistor 62 may be traced from the base, through resistor 63, the emitter-collector circuit of transistor 61, resistors 66 and 67, to ground. It should be noted that transistors 64 and 61 have equal control of the operation of switching transistor 62.

The pulses sent over conductor 57 to transistor 58 are then applied to the terminal 68 of free running multivibrator 14C. When transistor 55 is made non-conducting, a sharp negative pulse is sent to the base of transistor 58 and produces a sharp positive pulse at point 68 between two diodes 70 and 71 coupled to transistors 72 and 73. This pulse triggers the circuit and transfers conduction from one transistor to the other. The output of this circuit is applied to the base of transistor 64 by conductor 59. The curve showing the wave form produced by this circuit is shown in curve b, FIGURE 2.

The flasher circuit is further modified by the addition of circuit 14B which is a mono-stable multivibrator having transistors 74 and 75. The circuit is arranged so that transistor 74 is normally conducting while transistor 75 is non-conducting. A coupling between circuit 148 and circuit 14C is provided by conductor 76 which connects the collector of transistor '73 with the base of transistor 74 (through resistor 77 and capacitor 78). When transistor 73 conducts, a negative pulse is sent to the base of transistor 74 turning it otf. A short time interval later, which may be adjusted by resistor 79, conduction shifts back automatically to transistor 74. When transistor 74 is made non-conductive, 75 conducts, thereby lowering the voltage on its collector and conductor 80 and applying a negative bias to the base of transistor 81 making it non-conductive. The wave form produced by circuit 14C and transmitted over conductor 81 is shown in FIG- URE 2 by curve 0.

The conduction periods of transistors 61, 81 and 64 are shown in FIGURE 2 as curbes a, b and c, each showing the periods of conduction as positive pulses. Transistor 61 produces a series of non-conducting periods which are applied to gate transistor 62. Transistor 64 produces a similar series of non-conducting periods (of longer distribution) which are also applied to the same gate. The combination of the two results in the conduction characteristics shown in curve a+b in FIGURE 2. When the pulses of circuit 14C are added, the conduction characteristic is represented by curve a+b-|c.

The above described current pulses are applied to gate transistor 62 and are, in turn, amplified by transistor 82 and passing transistor 83 connected with its emitter-collector circuit in series between the positive terminal of the battery 10 and the positive lamp terminal 53. Passing transistor 83 operates as a gate to either pass current to operate the lamp 11 or cut it off completely.

In addition to the on-off characteristics of the circuit, a voltage regulator system is built into the control to provide a compensated voltage for the signal lamp 11 when the passing transistor 83 is conducting. Two voltage dividers are used to form a bridge circuit to produce an error voltage. One voltage divider includes a zener diode 84- and resistor 85. A second voltage divider includes resistors 86, 87 and 88. The junction point of zener diode S4 and resistor 85 is connected to the emitter of transistor 90, while a tap on resistor 87 is connected to the base.. In this manner the error voltage is applied to transistor 90 and is amplified by transistor 82 to control the resistance of passing transistor 83 during the period when the lamp 11 is lighted. Thermistors 91, 92 and 93 are added to the circuit to correct for changes in the transistor characteristics produced by changes in ambient temperature.

The lamp changer circuit operates by sensing the voltage drop across a series resistance 94 connected in series between the passing transistor 83 and the lamp terminal 53. However, this circuit operates only during the time the lamp 11 is lighted and during the dark intervals it is non-operative. Connections to resistor 94 are made by conductors 95 and 51 and are applied to the base and emitter of an amplifier transistor 96 which, in turn, is coupled to amplifying transistors 97, 98 and switching transistor 100 to deliver a strong signal current over conductor 101 to lamp changer device 16. Resistor 94 serves also to provide constant voltage regulation with varying output current. A thermistor 102 is added to the circuit for temperature compensation, and varistor 103 serves to reduce inductive surges caused by the operation of the lamp changer 16.

When lamp 11 is lighted, there is a voltage between conductors 51 and 95, transistor 96 is conductive and transistors 97, 98 and 100 are not conducting. When there is no load current, there is no voltage drop across load resistor 94, and the base and emitter of transistor 96 are at the same potential. This condition causes transistors 97, 98 and 100 to conduct and deliver a signal to the lamp changer.

It should be understood that the invention as herein disclosed comprises the several circuit components and their modifying connections. The details of each circuit have been described only to show one form of the inven tion as it may be constructed and operated.

Having thus fully described the invention, what is claimed as new and desired to be secured by Letters Patent of the United States, is:

1. A light sensitive circuit comprising; a photoconductive cell connected in series with a source of direct current for providing current therethrough, a first transistor including a collector, a base, and an emitter, said collector connected to a source of positive voltage in series with a first resistor, and said emitter connected to the negative terminal of said direct current source; a second transistor including a collect-or, a base, and an emitter, said second collector connected to the source of positive voltage in series with a second resistor, said second emitter connected to the negative terminal of the direct current source, a first voltage divider comprising a first plurality of series resistors connected between the collector of the first transistor and the negative terminal, a second voltage divider comprising a second plurality of series resistors connected between the collector of the second transistor and the negative terminal, a connection between the base of the first transistor and a first mid-point on the second voltage divider which applies a positive voltage to the first transistor base to render the first transistor non-conductive when the photg-conductive cell is non-conductive and for creating a positive feedback circuit which aids the transfer of conductance when the photo-conductive cell is rendered conductive by ambient light, a connection between the base of the second transistor and a mid-point on the first voltage divider which applies a reduced positive potential to the second transistor base to render the second transistor conductive when said cell is non-conductive, and a connection between the photo-conductive cell and a second midpoint on the second voltage divider which reduces the potential of the base in the first transistor to make it conduct when light is applied to the cell and current passes therethrough.

2. A light sensitive circuit as claimed in claim 1, wherein a capacitor is connected between said second mid-point of the second voltage divider and said negative terminal for absorbing short current pulses due to short light flashes incident on the photoconductive cell.

3. A light sensitive circuit comprising, a photo-conductive cell connected in series with a source of direct current for providing current therethrough, a cut off transistor including a base, a collector and an emitter, said collector and emitter connected in series with the photoconductive cell and the source of current, a passing transister including a base, a collector, and an emitter for passing current to a load, a load circuit connected to said source of current, said load circuit including the emittercollector electrodes of the passing transistor and a lamp for producing a light signal, a sequentially operating control circuit coupled between the base of the passing transistor and one side of the photo-conductive cell for interrupting the current to the load in accordance with a predetermined schedule, and a connection between a portion of the load circuit and the base of the cut off transistor for applying a control potential thereto to cut oil current fiow to the cell when the lamp is lighted.

4. A light sensitive circuit as claimed in claim 3, wherein a voltage regulator circuit containing a transistor and a zener diode is connected between the source of current and the photoconductive cell.

References Cited by the Examiner UNITED STATES PATENTS 1,959,170 5/1934 Marvin 250206 2,012,573 8/1935 Long 250-206 2,5 47,5 23 4/ 1951 Eicher 3'3 l-55 2,842,667 7/1958 Dench et al. 331-55 2,947,875 8/1960 Beck 2502l0 X 2,954,479 9/1960 Cibelius 250214 X 2,973,456 2/ 1961 Srnyth 250-214 X RALPH G. NILSON, Primary Examiner.

GEORGE N. WESTBY, WALTER STOLWEIN,

Examiners. 

1. A LIGHT SENSITIVE CIRCUIT COMPRISING; A PHOTOCONDUCTIVE CELL CONNECTED IN SERIES WITH A SOURCE OF DIRECT CURRENT FOR PROVIDING CURRENT THERETHROUGH, A FIRST TRANSISTOR INCLUDING A COLLECTOR, A BASE, AND AN EMITTER, SAID COLLECTOR CONNECTED TO A SOURCE OF POSITIVE VOLTAGE IN SERIES WITH A FIRST RESISTOR, AND SAID EMITTER CONNECTED TO THE NEGATIVE TERMINALS OF SAID DIRECT CURRENT SOURCE; A SECOND TRANSISTOR INCLUDING A COLLECTOR, A BASE, AND AN EMITTER, SAID SECOND COLLECTOR CONNECTED TO THE SOURCE OF POSITIVE VOLTAGE IN SERIES WITH A SECOND RESISTOR, SAID SECOND EMITTER CONNECTED TO THE NEGATIVE TERMINAL OF THE DIRECT CURRENT SOURCE, A FIRST VOLTAGE DIVIDER COMPRISING A FIRST PLURALITY OF SERIES RESISTORS CONNECTED BETWEEN THE COLLECTOR OF THE FIRST TRANSISTOR AND THE NEGATIVE TERMINAL, A SECOND VOLTAGE DIVIDER COMPRISING A SECOND PLURALITY OF SERIES RESISTORS CONNECTED BETWEEN THE COLLECTOR OF THE SECOND TRANSISTOR AND THE NEGATIVE TERMINAL, A CONNECTION BETWEEN THE BASE OF THE FIRST TRANSISTOR AND A FIRST MID-POINT ON THE SECOND VOLTAGE DI- 